Various embodiments of the present invention relate to disc storage systems and, in particular, to reducing the number of disc revolutions required during read retry operations.
In a disc drive, data is stored on one or more discs. A disc is typically divided into a plurality of generally parallel disc tracks, which are arranged concentrically with one another and perpendicular to the disc radius. Each track is further broken down into a plurality of sectors, which further aid in locating information.
The data is stored and retrieved by a transducer or xe2x80x9cheadxe2x80x9d that is positioned over a desired track by an actuator arm. Typically, when a read operation is sent from a host (such as a computer) to the disc drive, a controller converts a logical block address (LBA) received from the host to a physical block address (PBA). Next, the physical track, head and sector information, which includes the number of sectors to be read from a destination track, are calculated based on the PBA. A seek operation is then performed and sectors falling on the same track are usually read within a disc revolution. Data read from the disc is transferred to a buffer random access memory (RAM) inside the disc drive. When a read operation is started, as many sectors on the track can be read without stopping when buffer RAM is available. A read error, however, will cause the read operation to stop, and a retry attempt to be performed. Therefore, a disc read operation may include read and retry cycles to recover data from the number of sectors to be read. Retry cycles are required to recover data from sectors on which read errors are encountered (failed sectors).
It is common to encounter disc read-errors when the disc drive is transferring data from the disc to the buffer RAM inside the disc drive. Although all data sectors written to the disc have error correction bytes appended at the end of the data field to protect the data from any kind of error, sector errors may still happen under a typical noisy environment. Some errors occur momentarily due to system noise, thermal conditions or external vibrations. These errors are referred to as soft errors and can normally be recovered by attempting to read the failed sector repeatedly until data is successfully recovered. The worst case error is a permanent error which happens due to defects on the disc. These permanent, or hard errors, can never be recovered even after repeated read attempts. In either case (occurrence of a soft or hard error), a retry cycle is always initiated by the controller which tries various approaches to recover data from failed sectors.
In typical prior art systems, when an error is encountered during a disc read operation, the controller stops the read operation, applies a retry algorithm and then re-starts the read operation. Stopping the read operation for each read error encountered and performing a retry cycle on the failed sector results in extra revolution time (overhead) for the read operation.
Various embodiments of the present invention address these problems, and offer other advantages over the prior art.
Various embodiments of the present invention relate to disc storage systems that have a retry cycle which solves the above-mentioned problems.
A method and apparatus for reducing retry redundancy during disc read operations in a disc drive system are provided in which a number of physical sectors to be read from the disc during read operations is first determined. An attempt is then made to read all sectors of the number of sectors during a first disc revolution. Failed sectors of the number of sectors during the first disc revolution are also identified. A retry cycle is then performed on the failed sectors during a second disc revolution following the completion of the attempt to read all sectors of the number of sectors during the first revolution.
These and various other features as well as advantages which characterize various embodiments of the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.